1. Field of the Invention
The present invention relates generally to manhole cover technology and, more specifically, to a manhole system incorporating at least a uniquely configured cover, in addition to a likewise uniquely configured frame associated with the cover and separately secured to an upper extending end of a manhole wall. The system provides the advantages of more secure engagement and removal of the cover, and associated reduction in the occurrence of injury to a worker engaged in removing the cover. Additionally, an outwardly annular facing and tapered configuration of the frame results in a decrease of the likelihood of expansion and contraction forces exerted by the cement causing the cover and/or frame from projecting upwardly from a level surface established with the pavement.
2. Description of the Prior Art
The relevant art is well documented with various examples of manhole cover and construction assemblies. The manhole assembly typically includes such as a substantially level slab of concrete or pavement, exhibiting such as an annular central aperture communicating with a downwardly extending manhole wall, typically also of concrete construction.
Due to variances which may exist in the concrete, one application is prior art is directed to various types of leveling and height adjusting manhole assemblies. Included among these are references such as Heintz et. al., U.S. Pat. No. 6,371,687 which teaches a manhole covering frame leveling clip, attachable by friction fit to an exterior peripheral flange of a manhole cover frame. An adjustable bolt extends through the clip and in order to manipulate the height and angle of the frame so that the frame is in the same plane or elevation with the finished grade of a roadway surface. Other examples of height adjustable manhole assemblies include those disclosed in U.S. Pat. No. 6,520,713, issued to Sondrup and U.S. Pat. No. 5,470,172, issued to Wiedrich.
U.S. Pat. No. 4,203,686, issued to Bowman, teaches a liquid tight manhole closure structure exhibiting a base frame with an upwardly sloping and outwardly oblique surface adjacent an upper located and peripheral inner seat upon which a cover is seated. A retainer ring detachably secures the cover onto the frame and the ring and frame further exhibit peripheral coacting and detachably interlocking cam surfaces for removably securing the ring to the frame. A resilient sealant is disposed between the cover and the frame to prevent liquid seepage through the manhole opening. The sealant may further be vulcanized or otherwise secured directly to the periphery of the cover and/or to the frame.
Additional references, including U.S. Pat. No. 6,007,270, issued to Bowman, U.S. Pat. No. 6,371,688, issued to Yang et al., and U.S. Pat. No. 4,015,373, issued to Boissier, round out the teachings of the prior art. Bowman U.S. Pat. No. 6,007,270 teaches a lockable manhole frame assembly capable of supporting a member for obstructing a utility access opening (manhole cover) and which is in particular suitable for raising the level of the obstructing member to the level of such as a repaved roadway.
Yang U.S. Pat. No. 6,371,688 teaches a manhole cover mounting structure having an outer frame fastened to a manhole box by screw bolts and including an upright guide rod in each of a plurality of hollow peripheral locating blocks. An inner frame is adjustably fastened within the outer frame and in order to hold a cover plate in flush condition with a roadway surface. The inner frame includes a plurality of female screws fastened to peripheral lugs to hold a respective hollow screw rod for the mounting of through bolts, thereby securing the inner frame to the upright guide rod in each locating block of the outer frame.
Finally, Boissier U.S. Pat. No. 4,015,373 teaches a manhole assembly including a flat outer frame provided with an edge-section for receiving a single-piece manhole cover exhibiting three projections located at the apices of a triangle and which are adapted to rest on the edge-section so as to form a horizontal bearing triangle. The cover is further adapted to be locked within the frame and so as to prevent tilting of the cover about any one side of the bearing triangle under the action of a downwardly directed force applied to the cover externally of the triangle.
The present invention teaches a manhole system designed to overcome a number of shortcoming associated with the prior art manhole assemblies, and in particular incorporates a uniquely configured cover, in addition specified embodiments including a likewise uniquely configured frame associated with the cover and which is separately secured to an upper extending end of a manhole wall.
As previously explained, the manhole system provides the advantages of more secure engagement and removal of the cover, along with an associated reduction in the occurrence of injury to a worker engaged in removing the cover. Additionally, an outwardly annular facing and tapered configuration of the frame results in a decrease of the likelihood of expansion and contraction forces exerted by the cement causing the cover and/or frame from projecting upwardly from a level surface established with the pavement.
In a first preferred embodiment, a substantially annular shaped and three dimensional frame is provided and which is encased within the pavement slab such that a top edge extending surface of the frame lies substantially flush with a corresponding top edge surface of the slab. The frame, as previously described, includes in this embodiment the outer annular facing and tapered configuration such that the expansion and contraction forces of the adjoining concrete are directed in a substantially parallel and upwardly directed fashion, relative to the outer annular surface of the frame and to prevent the frame from being projected upwardly as a result of such forces.
An intermediate ring is supported upon an annular and recessed ledge defined in an inwardly and annular extending fashion within the frame. The ring in turn defines a recessed annular rim upon which a cover is seatingly engaged and supported and further such that an upper edge surface of the cover is substantially flush with the top edge extending surface of the ring and the frame.
Any plurality of locking fasteners are provided and are arrayed at an angle relative to a perpendicular axis extending through the cover and the ring. The locking fasteners are typically provided as interiorly threaded recesses, extending in a radially inward and downward fashion, and each of which receiving a threaded bolt displaceable between a locking position, in which the cover is rigidly secured to the ring and frame, and an unlocked position, in which the cover is removable. A further modification of the cover system incorporates the intermediate ring into the frame and such that the combination defines a single integral piece within which the cover is supported.
The cover, in either variant exhibits an upwardly and centrally extending sloping top surface. A pick hole is formed at an angle relative to a perpendicular axis extending through the cover and frame and such that a conventional tool can be engaged to unseat the cover. Additionally, a plurality of raised projections may be defined upon the top surface of the cover to facilitate fluid run-off. Also, one or more vertically extending bolts are threadably and recess seated at locations around a periphery of the cover and actuated downwardly to engage a corresponding top surface of the frame, in order to break a seal existing therebetween and to unseat the cover from the frame.
A yet further embodiment of the present invention contemplates either producing a manhole cover, as described above, for use in an existing and convention frame or, alternatively, of retrofitting or modifying an existing manhole cover for use in such an assembly. The cover, according to either sub-variant, includes the provision of at least the angularly defined pick hole, defined at an intermediate location along the body of the cover and which is best suited for receiving a pick or the like, as well as one or more radially outwardly and downwardly angled threaded recesses for receiving a lock bolt and for securely engaging the cover to an adjoining and inwardly facing wall of the existing frame.